CN110646378A

CN110646378A - Prism coupling system and method for characterizing curved parts

Info

Publication number: CN110646378A
Application number: CN201910958438.3A
Authority: CN
Inventors: A·刘; R·V·罗瑟夫; R·A·施奥特
Original assignee: Corning Inc
Current assignee: Corning Inc
Priority date: 2013-08-29
Filing date: 2014-08-28
Publication date: 2020-01-03
Anticipated expiration: 2034-08-28
Also published as: US10156488B2; JP2016535854A; US20150066393A1; KR102272826B1; TW201937141A; CN105705936A; JP6875459B2; TWI658261B; KR20160048926A; JP2019194613A; JP6549581B2; EP3039408A1; CN105705936B; WO2015031567A1; US10495530B2; CN110646378B; US20190025141A1; TWI746944B; TW201514457A; KR20210083393A

Abstract

Prism coupling systems and methods for characterizing curved parts (20) are disclosed. A coupling surface (44) of the coupling prism (40) interfaces with the curved outer surface of the curved piece to define a coupling interface (50). Measuring light is directed through the coupling prism and to the interface, wherein the measuring light has a width of 3mm or less. The TE and TM mode spectra reflected from the interface are digitally captured. These mode spectra are processed to determine at least one characteristic of the curved part, such as stress distribution, compressive stress, depth of layer, refractive index distribution, and birefringence.

Description

Prism coupling system and method for characterizing curved parts

The present application is a divisional application of the invention patent application having an international filing date of 28/08/2014, chinese national phase application number of 201480059343.3, entitled "prism coupling system and method for characterizing curved parts".

Cross Reference to Related Applications

The present application is based on its content and the content of which is incorporated herein by reference in its entirety, in accordance with the priority benefit of U.S. application S/N14/013,481 filed 2013, 8, 29.

Technical Field

The present disclosure relates to measuring stress in a part, and more particularly to a prismatic coupling system and method for optically characterizing a curved part.

Background

Chemically strengthened glass parts are becoming important for a variety of applications including: a resilient, shatter-resistant, scratch-resistant, touch-enabled, protective planar overlay window for smart phones and tablets. These glass parts are thinner, lighter and tougher than the tempered glass due to the high surface compression obtainable by the ion exchange process (e.g., at 8 x 10)⁸In the order of Pa).

The rapid non-destructive technique for measuring the two main parameters of stress profile (surface Compressive Stress (CS) and depth of layer (DOL)) has contributed to the rapid adoption, continued improvement and surprising market growth of such flat glass products. Such measurements may be made using commercially available high resolution prism coupling systems (such as FSM-6000LE manufactured by Orihara industries, ltd., japan and sold by Luceo). The third key parameter, Central Tension (CT), can be inferred by exercising a force balance requirement between compression and tension.

Prism-coupled systems capture the angular coupling spectra ("mode spectra") of the Transverse Electric (TE) and Transverse Magnetic (TM) optical propagation modes of the ion-exchange region. The stress is extracted from the difference between the two spectra by using the stress-optical coefficient (SOC). Due to small SOC (-3 x 10)^–6RIUMPa, where RIU stands for refractive index unit), the stress-induced portion of the refractive index represents the small difference between the two larger refractive index values. Thus, small errors in the recovered TE and TM distributions strongly affect the size and shape of the stress distribution. To minimize this error, high resolution capture of the TE and TM mode spectra is necessary.

The excellent strength properties of chemically strengthened glass parts make them desirable to replace existing curved glass parts (such as cuvettes) and to replace non-planar exterior glass or plastic parts of personal electronic devices. However, such rapid non-destructive measurement of TE and TM mode spectra on curved parts has proven problematic for the purpose of measuring one or more characteristics, such as stress distribution or some of its critical parameters.

Disclosure of Invention

One aspect of the present disclosure is a method for determining at least one characteristic of a curved part having a curved outer surface. The method includes interfacing a coupling surface of a coupling prism with the curved outer surface to define a coupling interface. The method also includes directing measurement light through the coupling prism and to the interface, wherein the measurement light has a width of 3mm or less. The method further includes digitally capturing TE and TM mode spectra reflected from the interface. The method also includes processing the TE and TM mode spectra to determine at least one characteristic of the curved part. In an example, the at least one characteristic is selected from a group of characteristics comprising: surface stress, stress distribution, compressive stress, depth of layer, refractive index distribution, and birefringence.

Another aspect of the present disclosure is a method for determining at least one characteristic of a curved part having a curved outer surface. The method comprises the following steps: directing the focused measurement light to a coupling prism assembly having a coupling prism interfacing with an outer surface of a curved part to define a coupling interface, wherein the curved outer surface is defined by a radius R1 ≧ 0.5mm and a radius R2 ≧ 20 m; reflecting the measurement light from the coupling interface while constraining the measurement light to have a width of 3mm or less prior to the reflecting; detecting the reflected measurement light to obtain TE and TM mode spectra; and processing the TE and TM mode spectra to determine at least one characteristic of the curved part.

Another aspect of the present disclosure is a prismatic coupling system for determining at least one characteristic of a curved part having a curved outer surface. The system comprises: a light source system that generates measurement light; a coupling prism assembly having a coupling prism with input and output surfaces and a coupling surface that interfaces with the curved outer surface to define a coupling interface, wherein the coupling prism assembly includes means for defining a width of measurement light to be 3mm or less; a detector system arranged to receive measurement light reflected from the interface and exiting the output surface to digitally capture TE and TM mode spectra; and a controller for processing the TE and TM mode spectra to determine at least one characteristic of the curved part.

Additional features and advantages will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments as described in the detailed description, the claims, and the appended drawings. It is to be understood that both the foregoing general description and the following detailed description are exemplary and are intended to provide an overview or framework for understanding the nature and character of the claims.

Drawings

The accompanying drawings are included to provide a further understanding of the specification, and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiments and, together with the description, serve to explain the principles and operations of the embodiments. As such, the present disclosure will be more fully understood from the detailed description given below, taken in conjunction with the accompanying drawings, in which:

FIG. 1A is an isometric view of an example curved part;

FIG. 1B is a cross-sectional view of the curved part of FIG. 1 as taken in the x-y plane and showing a first radius of curvature (R1) and an ion exchange region having a depth of layer (DOL);

FIG. 1C is a cross-sectional view of the curved part of FIG. 1A as taken in the y-z plane and showing a second radius of curvature (R2);

FIG. 1D is similar to FIG. 1A and shows an example of an ideal cylindrical part with a second radius of curvature of infinity;

FIG. 2 is a schematic diagram of an example embodiment of a prismatic coupling system that may be used to measure the mode spectrum of a curved part using the methods disclosed herein;

FIG. 3A is an enlarged view of an exemplary photodetector system of the prism-coupled system of FIG. 2, showing the TE/TM polarizer and the detector;

FIG. 3B is a schematic illustration of TE and TM mode spectra captured by the photodetector system of FIG. 3A using the prism-coupled system of FIG. 2;

FIG. 4A is a close-up view of an example coupling prism assembly of the prism coupling system of FIG. 2, showing a coupling prism and a light-constraining member disposed adjacent to the coupling prism input surface and having a narrow slot that constrains light available on the prism coupling surface to a narrow spatial region that is not limited to the z-direction;

FIG. 4B is similar to FIG. 4A and shows the light-constraining member disposed adjacent to the input surface rather than the input surface;

FIG. 4C is a top view of the coupling prism as arranged in FIG. 4A or FIG. 4B, showing the long and narrow regions of optical contact defining the part-prism coupling interface, and showing the illumination area formed by the measuring beam;

FIG. 4D is an elevation view of the illumination area of FIG. 4C, showing the y-z plane and having an out-of-plane angle

Example exit surface beams (e.g., projected onto an x-z plane);

FIGS. 5A and 5B are elevation and elevation views of the example light-constraining member of FIGS. 4A and 4B;

FIG. 6A is an elevation view of an example coupling prism, where the input and output surfaces include opaque regions that define slit openings;

FIG. 6B is an elevation view of an example coupling prism having a curved portion on the coupling surface;

FIG. 6C is an elevation view of an example coupling prism incorporating features of the coupling prisms of FIGS. 6A and 6B;

FIG. 7A is an example coupling prism including a thin prism supported by two opaque light absorbing blocks;

FIG. 7B is similar to FIG. 7A and shows an example of a coupling prism having a curved coupling surface;

FIG. 7C is similar to FIG. 7B and shows an example in which the coupling prism has a top and an alternative concave flat cylindrical lens portion defining a curved coupling surface; and

FIG. 8 is a top view of an example alignment fixture for holding and aligning finite diameter and finite length curved parts within the prismatic coupling system of FIG. 2.

Any coordinates and axes shown in some of the figures are for reference and are not intended to be limiting as to direction or orientation. Additionally, references to directions such as "vertical" and "horizontal" are used for ease of discussion with respect to select features in a given figure and are not intended as limitations on direction or orientation.

Detailed Description

Reference will now be made in detail to the various embodiments of the disclosure, examples of which are illustrated in the accompanying drawings. Wherever possible, the same or similar reference numbers will be used throughout the drawings to refer to the same or like parts. The drawings are not necessarily to scale and one skilled in the art will recognize where in the drawings has been simplified to illustrate key aspects of the disclosure.

The claims set forth below are incorporated into and constitute a part of this detailed description.

The entire disclosure of any publication or patent document referred to herein is incorporated by reference, including U.S. patent applications S/N13/463,322 and 61/706,891.

Bending part

FIG. 1A is an isometric view of an example curved part 20, and FIG. 1B is a cross-sectional view of the curved part taken in the x-y plane. The curved part 20 has a body 22 and a curved outer surface 24. In the exampleThe curved part 20 is made of glass and has a base (or bulk) refractive index n_s. Fig. 1A shows a cartesian coordinate system, along with polar coordinates (r, θ). FIG. 1C is a cross-sectional view of curved part 20 taken in the y-z plane. In an example, the curved part 20 may be a rod, or it may be a tube with a hollow interior. In the example, the curved part 20 has a central axis a 0.

The outer surface 24 of the curved part 20 has a first radius of curvature R1 in the x-y plane and a second radius of curvature R2 in the y-z plane. In an example, the first radius of curvature R1 may be relatively small while the second radius of curvature R2 is relatively large. In the example, the first radius of curvature R1 is 0.5mm or more, and the second radius of curvature R2 is 20m or more. In the example of the curved part 20 shown in fig. 1D, the second radius of curvature R2 ∞ is such that fig. 1D is a cylinder. The curvature may be outward as shown by way of example, or may be inward. The first and second radii R1 and R2 are used herein to describe the inward or outward curvature.

In the example where the second radius of curvature R2 ≠ infinity, the second radius of curvature R2 is sufficiently large compared to the first radius of curvature R1 that the curved part 20 is substantially cylindrical or conical in a portion of its surface for making mode spectral measurements. The second radius of curvature R2 is dictated in part by the dimensions of coupling prism 40 (introduced and discussed below in connection with fig. 2). In an example, the second radius of curvature R2 is many times longer in the z-direction than the length of the coupling prism 40.

And in examples, the first radius of curvature R1 need not be constant, as in the case of a conical surface. Curved part 20 may also have complex surfaces, such as a combination of flat and curved portions, with a simple curved part shown in the figures for ease of illustration.

In an example, the curved part 20 is made of glass that is subjected to an ion exchange process, wherein at least one type of ions has been exchanged through the outer surface 24 into the body 22. The ion exchange process defines an ion exchange region 25 (fig. 1B and 1C), the ion exchange region 25 having a refractive index profile n (r) that may be different for s-polarized (transverse electric, TE) light and p-polarized (transverse magnetic, TM) light, the p-polarized light being polarized parallel to its plane of incidence.

The (radial) depth of the ion exchange region 25 as measured directly inward from the outer surface 24 (i.e., in a direction perpendicular to the outer surface 24) is referred to as the "depth of layer" or DOL. An example range of DOL is from 5 to 150 microns. DOL is typically less than half the thickness of the sample, including the case where the sample is a hollow tube and the sample thickness is represented by the thickness of the tube wall.

The ion exchange process that forms the ion exchange region 25 in the curved part 20 can promote birefringence B at or near the outer surface 24 of the curved part 20. This birefringence B can be used to calculate the stress (e.g., compressive stress CS) and/or stress distribution s (r) at (or near) the outer surface 24 using known techniques. The stress distribution is related to the birefringence B via s (r) ═ B (r)/SOC, where SOC is the stress-optical coefficient and B (r) ═ n_TM(r)–n_TE(r)]。

The spectra of the optical modes (i.e., TE and TM mode spectra) of the curved part 20 cannot be properly imaged and captured using existing prism coupling based optical instruments for measuring planar parts. When the curved part 20 is in contact with the prior art coupling prism, the image of the optical angular spectrum (i.e., the TE, TM mode spectrum) becomes blurred and sometimes distorted. This makes automatic identification of the effective refractive index of the guided optical mode problematic, which in turn makes accurate determination of one or more characteristics (e.g., stress distribution s (r)) that rely on such measurements problematic.

In experiments, a conventional prism coupling system (e.g., FSM-6000LE prism coupling instrument manufactured by Orihara industries, ltd., tokyo, japan) was used to measure stress in cylindrical glass samples having a first radius of curvature, R1 ═ 8.5mm and R2 ∞. Dark lines corresponding to coupling into TE and TM modes guided in the near surface waveguide region defined by ion exchange region 25 can be observed only if the sample is precisely aligned such that the axis of the cylinder under test and the contact line between the cylinder and the coupling surface of the prism lie in a plane orthogonal to the prism facets for optical input and output.

In addition, even with optimal alignment, the dark line of the mode spectrum is very wide and very dim compared to the apparent high contrast lines typically observed during measurement of flat glass samples with near-surface planar waveguides. Due to insufficient spectral line contrast, the captured mode spectral images cannot be automatically processed with commercial FSM-6000LE system software to obtain stress parameters. Manual detection of spectral line positions of mode spectral images results in significant errors due to poor contrast and due to the strong dependence of the image pattern on sample alignment.

Prism coupling system for measuring curved parts

FIG. 2 is a schematic diagram of an exemplary prism-coupled system ("system") 10 suitable for use in measuring a mode spectrum of a curved part, such as curved part 20. The system 10 includes a coupling prism assembly 38, discussed in more detail below. The system 10 includes optical axes a1 and a2 that intersect at the coupling prism assembly 38.

System 10 comprises, along axis a1, in succession: a light source emitting measurement light 62 of wavelength λ; an optional optical filter 66, optionally contained in the detector path on axis a 2; an optional light scattering element 70; and an optional focusing optical system 80, forming focused (measurement) light (beam) 62F, as explained below. Thus, in the example of the system 10, there are no optical elements between the light source 60 and the coupling prism assembly 38. The light source 60, optional filter 66, optional light scattering element 70, and optional focusing optics 80 constitute an example light source system 82 that produces focused measurement light 62F.

The system 10 further comprises, in order from the coupling prism assembly 38 along axis a 2: a condenser optical system 90 having a focal plane 92 and a focal length f and receiving reflected light 62R (explained below); a TM/TE polarizer 100 having TM and TE polarizing portions 100TE and 100 TM; and a photodetector system 130. Axis a1 defines the center of the optical path OP1 between the light source 60 and the coupling prism assembly 38. The axis A2 defines the center of the optical path OP2 between the coupling prism assembly 38 and the photodetector system 130. The collection optics 90, TM/TE polarizer 100, and photodetector system 130 constitute an exemplary detection system 140.

Detection system 140 may also include apertures 136 on either side of collection optics 90. The aperture 136 may be configured to reduce the amount of "over-coupled" light detected by the photodetector system 130. Here, "over-coupled light" is reflected light 62R from the coupling prism 40 that does not represent the actual TM and TE mode spectra, as explained in more detail below.

Fig. 3A is a close-up view of the photodetector system 130. In an example, the photodetector system 130 includes a detector 110 (e.g., a CCD camera) that can be replaced with an IR analog detector and frame grabber 120 (see fig. 2) for wavelengths longer than 1100 nm. In other embodiments discussed below, the detector 100 comprises a CMOS detector or one or two linear photodetectors (i.e., a line of integrated photodiodes or photo-sensing elements). The detector 110 may also include one or more microbolometers, microbolometer cameras, one or more InGaAs-based photodetectors, or InGaAs cameras.

The detector 110 includes a photo sensitive surface 112. The photo-sensitive surface 112 is substantially present in the focal plane 92 of the collection optics 90, substantially perpendicular to the axis a 2. This serves to convert the angular distribution of the reflected light 62R exiting the coupling prism assembly 38 into a lateral spatial distribution of light at the sensor plane of the detector 110.

The separation of the photo-sensitive surface 112 into TE and TM portions 112TE and 112TM allows a digital image of the angular reflection spectrum (including the mode spectrum) to be simultaneously recorded by the detector 110 for the TE and TM polarizations of the reflected light 62R. This simultaneous detection eliminates the source of measurement noise that may be caused as TE and TM measurements are made at different times, assuming that the system parameters drift over time.

FIG. 3B is a schematic diagram of TE and TM mode spectra captured by the exemplary detector system of FIG. 3A. For purposes of illustration, the TE and TM mode spectra are shown as having high contrast.

Example light sources 60 include visible or infrared lasers, visible or infrared light emitting diodes, visible or infrared Amplified Spontaneous Emission (ASE) sources, visible or infrared Super Luminescent Diode (SLD) sources, and wider bandwidth sources such as thermal filament lamps and quartz lamps combined with appropriate means of narrowing the spectrum, including wavelength selective filters or diffraction gratings. Example operating wavelengths λ of light 62 generated by light source 60 include visible wavelengths (such as 405nm,488nm,590nm,633nm) and infrared wavelengths (such as (nominal), 820nm,940nm,1,060nm,1,550nm,1,613nm,1,900nm, or 2,200 nm).

When combined with a photodetector system 130 sensitive at the wavelength λ of the light source, and when encompassing appropriate narrowing of the spectrum, any light source 60 of the above-listed type having a dominant wavelength ranging from 400nm to 2200nm and sufficient brightness may be configured to implement the measurement method disclosed herein. The required brightness depends on the sensitivity of the detector 110 and the noise equivalent power, including the fundamental detector noise, as well as external electrical noise or background light.

The system 10 includes a controller 150 that may be configured to control the operation of the system. The controller 150 is also configured to receive and process (image) signals SI from the photodetector system 130, which signals SI represent the captured TE and TM mode spectral images. The controller 150 includes a processor 152 and a memory unit ("memory") 154. The controller 150 may control the activation and operation of the light source 60 via a light source control signal SL and may receive and process an image signal SI from the photodetector system 130 (e.g., from the frame grabber 120, as shown). In one embodiment, the TE and TM spectra may be collected sequentially, where the TE/TM polarizer 100 may comprise a single portion that transmits only a single polarization. In this case, the polarizer may be rotated between two orientations having a 90 ° difference in polarization direction, and the controller 150 may control the switching of the polarizer between the two orientations and the synchronization of this switching with the sequential collection of TE and TM spectra.

In one example, the controller 150 comprises a computer and includes a reading device, e.g., a floppy disk drive, a CD-ROM drive, a DVD drive, a magneto-optical disk (MOD) device (not shown), or any other digital device including a network-connected device, such as an ethernet device (not shown), for reading instructions and/or data from a computer-readable medium, such as a floppy disk, a CD-ROM, a DVD, a flash drive, or another digital source, such as a network or the internet. The controller 150 is configured to execute instructions stored in firmware and/or software (not shown), including signal processing instructions, for performing the surface birefringence/stress measurements disclosed herein. In an example, the terms "controller" and "computer" are interchangeable.

Controller 150 may be programmed to perform the functions described herein, including the operation of system 10 and the aforementioned signal processing of image signal SI, to derive a measurement of at least one characteristic of the curved part under test, such as surface stress, stress distribution, compressive stress, depth of layer, refractive index distribution, and birefringence.

As used herein, the term computer is not limited to just those integrated circuits referred to in the art as a computer, but broadly refers to a computer, a processor, a microcontroller, a microcomputer, a programmable logic controller, an application specific integrated circuit, and other programmable circuits, and these terms are used interchangeably herein.

The software may implement or facilitate the performance of the operations of the system 10 as disclosed herein, including the aforementioned signal processing. Software may be operatively installed into the controller 150, particularly in the processor 152 and memory 154. Software functions may involve programming including executable code, and these functions may be used to implement the methods disclosed herein. The software codes may be executed by a general purpose computer, such as by processor 152.

In operation, the code and possibly associated data records are stored within the general computer platform, within processor unit 152, and/or in local memory 154. At other times, however, the software may be stored at other locations and/or shipped for loading into a suitable general-purpose computer system. Embodiments discussed herein relate to one or more software products in the form of one or more code modules carried by at least one machine-readable medium. Execution of such code by the processor 152 of the computer 150 enables the platform to implement the directory and/or software download functionality substantially in the manner performed in the embodiments discussed and illustrated herein.

Computer 150 and/or processor 152 may each employ a computer-readable medium or machine-readable medium (e.g., memory 154), referring to any medium that participates in providing instructions to the processor for execution (e.g., determining an amount of surface birefringence/stress or stress distribution s (x)) of curved part 20. The memory 154 constitutes a computer-readable medium. Such a medium may take many forms, including but not limited to, non-volatile media, and transmission media. Non-volatile media includes, for example, optical or magnetic disks, such as any of the storage devices in any computer operating as one of the server platforms discussed above. Volatile media includes dynamic memory, such as the main memory of such a computer platform. Physical transmission media include coaxial cables, copper wire and fiber optics, including the wires that comprise a bus within a computer system.

Thus, common forms of computer-readable media include: for example, floppy disks, flexible disks, hard disks, magnetic tape, flash drives, and any other magnetic medium; CD-ROM, DVD, and any other optical media; less common media such as punched cards, paper tape, and any other physical media with a pattern of holes; RAM, PROM, EPROM, FLASH-EPROM, and any other memory chip or cartridge; a carrier wave propagating the data or instructions, a cable or link propagating such a carrier, or any other medium from which a computer can read programming code and/or data. Many of these forms of computer readable media may be involved in carrying one or more sequences of one or more instructions to processor 152 for execution.

The system 10 may be a modified version of the aforementioned commercial prism coupling instrument (such as the FSM-6000LE prism coupling instrument manufactured and sold by Orihara industries, ltd, tokyo, japan).

Coupling prism assembly

Fig. 4A and 4B are side views of an example configuration of a coupling prism assembly 38, the coupling prism assembly 38 being shown mated with the example curved part 20 and including the example light-confining member 200. Fig. 5A and 5B are an elevation view and a front view of the example light-constraining member 200 of fig. 4A and 4B.

The coupling prism assembly 38 includes a coupling prism 40 having an input surface 42, a coupling surface 44, and an output surface 46. Coupling edgeThe mirror 40 has a refractive index n_p>n_s. Coupling prism 40 interfaces with curved part 20 by bringing coupling prism coupling surface 44 into optical contact with a portion of curved outer surface 24. Fig. 4C is a top view of the coupling prism 40 of fig. 4A and 4B, and shows long and narrow regions of optical contact between the part outer surface 24 and the coupling surface 44, defining long and narrow part-prism coupling interfaces ("interfaces") 50.

Fig. 4C also shows an illumination area 62L formed by the measuring beam 62F. In an example, illumination region 62L and interface 50 are elongated and substantially aligned along their respective long axes. Fig. 4D is an elevation view of illumination area 62L showing the y-z plane and "out of plane"

light beams

62F and 62R.

Indicating the face angle. Illumination area 62L has w_LIs measured in the x direction. The example illumination region 62L is shown as having a constant width w_LBut w_LAs well as the length of the illumination area.

In the example, the refractive index n_fIs used to facilitate optical coupling between the coupling prism 40 and the curved part 20 and forms part of the interface 50. In the example, n_p≥n_f>n_s。n_f1.64. In other examples, the interfacing fluid refractive index n_f＝n_pPlus or minus 0.02. In a particular related example, the prism refractive index may be n_p＝1.72。

The coupling prism assembly 38 of fig. 4A and 4B includes the aforementioned example light confinement member 200 adapted to interface with the coupling prism 40 at either the input surface 42 (fig. 4A) or the output surface 46 (fig. 4B). The example light-confining member 200 is a truncated right-angle prism made of an opaque material or having an opaque coating. The light-confining member 200 has an angled front surface 202, a truncated top surface 204, a back surface 206, a bottom surface 208, and parallel sides 210. The light-confining member 200 has a height h1, a base length l1 at the bottom surface 208, a top length l2 at the truncated top surface 204, and a width w, as shown. The bottom surface 208 and the angled front surface 202 define an angle α.

The light-confining member 200 includes a central groove 220 that is open at the surfaces 202, 204 and 206. The central groove 220 has an inner surface 222 and a bottom 224 that resides above the bottom surface 208 to have a height h2< h 1. In one example, the inner surface 222 is parallel to the sides 210 to define a slot 220 having a uniform width s. In other examples, the central slot 220 may be configured to have a width s that varies along its length (e.g., linearly or in a curved manner). The slot width s may be selected to define various degrees of light confinement. In an example, the inner surface 222 of the groove 220 has a light absorbing coating, e.g., is darkened, oxidized, anodized, or the like, to reduce specular and diffuse reflection.

Example values of dimensions of the example light confining member 200 are set forth in table 1 as follows:

in an example, one or two light-constraining members 200 are arranged relative to the coupling prism 40 to constrain the illumination area 62L to the long and narrow interface 50 and to constrain the

light beams

62F and 62F to have narrow angles outside the y-z plane

(ii) range (fig. 4D). In an example, the size and angle of the illumination area 62L

Is defined by the width s of the central slot 220. In an example, one or both light-constraining members are disposed proximate to the input and/or

output surfaces

42 and 46 of the coupling prism 40. In another example, one or both light-constraining members are spaced apart from the input and/or

output surfaces

42 and 46 of the coupling prism 40.

The mode spectral image captured by the photodetector system 130 (see, e.g., fig. 3B) represents the angular spectrum of the TM wave reflected from the interface 50. The bright areas on the image correspond to high reflectivity, while the dark lines correspond to the coupling of the measurement light 62F into the guided or sometimes well-defined leaky modes. The extended dark regions are typically associated with coupling of leaky and radiative modes into the substrate. Experiments performed using the light-constraining member 200 in the coupling prism assembly 38 in the system 10 resulted in several times increase in the contrast and sharpness of the TE and TM mode spectra compared to the unconstrained effective illumination and 5mm (0.197 inch) collection width with the unconstrained prism assembly supplied to a conventional FSM-6000LE instrument.

The experiment on the example curved part 20 included capturing a mode spectrum image of a sample having a DOL of a first radius of curvature R1 ═ 8.5mm and 23 micrometers. The mode spectrum image shows an observable improvement in contrast for a slot width s <3mm and an even greater improvement for a slot width s <1.5mm, as compared to the mode spectrum contrast for a standard collection width of 5 mm. From these observations and dimensions of the light-constraining member 200 described above, and those of the coupling prism 40, an improvement in mode spectral contrast can be obtained when the prism coupling surface 44 is illuminated by a focused beam 62F that is narrowed to about 3mm or less.

Contrast improvement during measurement of curved parts may also be observed when the beam 62F incident on the prism assembly 38 has projections in the plane of the prism coupling surface 44 that are constrained to subtend an angle less than about 10 ° relative to a line of symmetry of the illumination strip that is designed to coincide with the line of contact between the curved portion of the curved part 20 and the prism coupling surface 44.

The improvement in contrast of the mode spectra is due in part to rejection of light that does not interact with the sample. This light rejection is already considerable when the slot width s in the described experiments is in the range of 1.5mm to 3 mm. For even smaller slot widths s, there may be even greater improvement. The contrast improvement is also due in part to rejection of light rays whose projection in the plane of the coupling surface 44 forms a large angle with the sample prism contact line defining the interface 50.

For large slot widths s, this can be achieved by a detection system typically provided in the system 10An aperture 136 (see fig. 2) or other aperture in the system 140 blocks these unwanted light rays. Thus, the improved angular component due to the light-confining member 200 is related to the slot dimension s<1.5mm becomes more pronounced, for example, light rays 62R passing through the prism assembly 38 and reaching the photodetector system 130 have an angle in the plane of the coupling surface 44 that is constrained to less than about 5In the case of projection of (2). Note that in some cases, the projection angle of the reflected rays from beam 62R after interaction with the curved surface of the sample

Angle of projection of corresponding incident light from beam 62FSlightly different.

Thus, illumination that may be placed near or far from coupling prism 40 and constrained so that

(especially

) Any combination of grooves, or apertures (e.g., such as aperture 136) may contribute to improving the contrast of the measured mode spectrum.

Is defined as the angular range of

And is limited to 20 in the example or 10 in the narrower example.

Width w of illumination area 62L_LAnd an angular range associated with the illumination area

Can be tied byAt least two apertures of the system 10. In the example described above, the two apertures are the input and output ends of the slot 220 at the front surface 202 and the back surface 206 of the light-confining member 200 (see, e.g., fig. 5A). In other examples, one of the apertures may be part of the detection system 140, such as aperture 136, for reducing contrast reduction due to parasitic unwanted illumination and also "over-coupling" effects, where some of the focused light 62F is resonantly coupled into and out of the curved part 20 as follows: when the reflected light 62R reaches the photodetector system 130, it increases the light intensity at the location (e.g., at an angle) where the dark line should be observed.

Thus, one aperture in the system 10 may be the slot 220 of the light-confining member 200, with the other aperture defined by a single slit or confined opening that is increased to define the width of the illumination region 62L. Such apertures in standard prism-coupled systems are typically too large to effectively help improve the mode spectral contrast for measuring curved parts. For a radius of curvature R1<10mm, in the example, the two apertures are defined by the slots 220 at the front end 202 and the rear end 206 of the light-confining member 200.

When measuring curved part 20 in system 10, reflected light 62R is sent from the entire coupling surface of the prism toward photodetector system 130. With respect to this signal, only a small portion of the reflected light 62 is reflected from the long and narrow interface 50. The measurement light 62F, which interacts with regions of the curved part 20 that are substantially separated from the coupling prism 40 and gradually curved away from the coupling prism, broadens or deviates outside the field of view of the photodetector system 130. This is identified as one cause of surprising contrast degradation in the mode spectrum when the curved part 20 is measured using a conventional prism-coupling measurement system.

Further examples of coupling prism assemblies

Fig. 6A is an elevation view of an exemplary coupling-prism assembly 38 in which the input surface 42 and output surface 46 of the coupling prism 40 include respective

opaque portions

42a, 42b and 46A, 46b that define slits 47 and 48 through which light can pass. In an example,

opaque portions

42a, 42b and 46a, 46b are defined by an absorbing layer formed on opaque portions of input surface 42 and output surface 46.

Slits

47 and 48 may be defined using conventional masking techniques. In another example,

opaque portions

42a, 42b and 46a, 46b may be separate plates or films placed in close proximity (i.e., in close contact or slightly spaced apart) to input surface 42 and output surface 46. The

slits

47 and 48 serve as the central slot 220 of the light confining member 200 for the same purpose to define the width of the measurement light 62 and may also be referred to as "slots" for consistency of terminology.

In the embodiment of fig. 6A, the slot is formed by two

slits

47 and 48, one near or on the input prism surface and one near or on the output prism surface. Fig. 6A shows yet another embodiment in which the coupling prism 40 contains three regions, where the central region 48 is transparent at the measurement wavelength, while the regions on either side thereof are strongly absorbing at the measurement wavelength. Such a coupling prism 40 can be obtained by fusing together three prisms made of the same or similar glass, where the two outer glasses are doped with iron or other absorbing ions and possibly annealed in a reducing environment to enhance the absorption at the measurement wavelength.

FIG. 6B is similar to FIG. 6A and shows an example coupling prism 40, where coupling surface 44 includes a cylindrically curved portion 44C, which cylindrically curved portion 44C is curved inward in the example and has a radius of curvature of about R1 (i.e., -R1). This particular coupling prism 40 may be advantageously used in coupling prism assemblies 38 in conjunction with light blocking features, such as one or more light-restricting members 200 or

opaque portions

42a, 42b and/or 46a, 46 b. In an example, the radius of the curved portion 44C is between approximately 0.5R1 and 1.5R 1. In the example, with n_f>n_sParticularly where the radius of the curved portion of the part 20 is less than R1.

Fig. 6C shows an example coupling prism 40 that combines features of the coupling prisms of fig. 6A and 6B, such that the resulting coupling prism has a cylindrically curved portion 44C and opaque portions 42a, 42B and 46A, 46B. In the example, the cylindrical curved portion 44C has a width substantially the same as the width of the slit 48. In another example, the cylindrically curved portion 44C is wider than the slit 48.

Fig. 7A is an elevation view of another exemplary embodiment of a coupling prism assembly 38, the coupling prism assembly 38 comprising a narrow coupling prism 70 sandwiched by two masses 250. The block 250 is opaque and may be part of a single block of opaque material or two separate blocks. The block 250 thus defines a narrow slot 252 in which the narrow coupling prism 40 resides. In examples, the faces of the block 250 facing the narrow coupling prism 40 have strong light absorption at the measurement wavelength, or may be coupled to the prism using glue or other material having strong light absorption at the measurement wavelength.

The example narrow coupling prism 40 has a width of about 3mm or less and in an example has a width of about 2mm or less. The lower limit on the width of the narrow coupling prism 40 is defined by adverse scattering and diffraction effects, in the example, the width is less than about 0.2 mm. In an example, the block 250 may include mounting and alignment features 254 for mounting and aligning the coupling prism 40 relative to the block. In the example, the narrow slot 252 present in the coupling prism 40 ensures the required light confinement for good mode spectral contrast and proper alignment with respect to the rest of the system 10.

Fig. 7B is similar to fig. 7A except that the coupling surface 44 of the coupling prism 40 is curved and has, in particular, a generally cylindrical concave curvature. In an example, the radius of curvature of the curved coupling surface 44 is similar to the first radius of curvature R1 of the curved part 20 to be measured and may be slightly larger in an example. The use of a concave cylindrical coupling surface 44 allows for self-alignment of the curved part 20 for measurement and can significantly reduce measurement time.

Fig. 7C is similar to fig. 7B and shows an example coupling-prism assembly 38 in which the coupling prism 40 includes a thin prism portion 40T having a flat base 44F and an alternative concave flat cylindrical lens portion ("cylindrical lens") 44L that interfaces with the flat base 44F and defines a curved coupling surface 44. In an example, at least a portion of the cylindrical lens 44 is held by the block 250. In examples, the thin lens portion 40T is held by the block 250 via an adhesive, an index matching oil, a vacuum, or by optical contact.

Alignment jig

Successful measurement of stress in the curved part 20 requires a mode spectrum with sufficient contrast, which in turn requires precise alignment of the coupling prism 40 with respect to the curved part. Specifically, the coupling prism 40 needs to contact the outer surface 24 of the curved part 20 in the following manner: this approach matches the illumination area 62L (fig. 5A) defined by the central slot 220 of the light-confining member 200, the slits 47 and 48 (fig. 6A) defined by the

opaque portions

42a, 42b and 46A, 46b, or the narrow slot 252 (fig. 7A) defined by the block 250 and the narrow coupling prism 40. A slight angular misalignment (<1 °) leads to a tilt of the spectral line (fringe), resulting in measurement errors. A large angular misalignment (only a few degrees) results in blurring and even disappearance of the fringes.

For coupling prism assemblies 38 that do not provide alignment of the curved parts 20, an alignment fixture can be used for such alignment while allowing precise positioning and angular alignment of the curved parts to optimize the measured mode spectral contrast.

FIG. 8 is a top view of an example alignment fixture 300 for holding and aligning curved part 20 relative to coupling prism 40. The alignment fixture 300 is configured to interface with the coupling prism assembly 38. The alignment fixture 300 includes a rectangular outer frame 310 having an interior 312, the interior 312 being defined by opposing vertical interior side walls 314 and opposing horizontal interior side walls 316. Alignment fixture 300 includes spaced apart and parallel horizontal guide members 320 disposed within frame interior 312 and having ends 322 configured to slide along or within vertical interior sidewalls 314, e.g., in tracks (not shown). The horizontal guide member 320 has opposing inner surfaces 324.

The alignment fixture 300 further comprises a vertically arranged support column 330 fixed to the lower guide member 320 and passing through the upper support member such that the latter can be translated vertically along the support column. Each support post 330 has an end 332 that interfaces with a corresponding resilient member 340 on the top vertical inner sidewall 314 of the frame 310. Inner surface 324 of horizontal guide member 320 includes a resilient member 326 for engaging outer surface 24 of curved part 20 without damaging the curved part. The example cylindrical curved part 20 (dashed line) is shown as being held by a resilient member 326.

The alignment fixture 300 further includes alignment screws 350 that pass through the threaded portion of the outer frame 310 to engage the lower support member 320. The alignment screw 350 may be used to push the lower support member 320 toward the upper support member, thereby compressing the curved piece 20 between the resilient members 326. The elastic member 340 allows the upward movement of the lower support member 320 by compression while also serving as a force buffer for hindering the upward movement of the upper support member, thereby maintaining the parts aligned in the direction indicated by the screw 350. The alignment screw 350 can also be used to provide a selected orientation of the curved part 20 within the frame interior 312 and relative to the coupling prism 40 when the alignment fixture 300 is mated with the coupling prism assembly 38.

To reduce coupling between rotation and lateral displacement of the curved features 20, the alignment fixture 300 may be positioned such that the coupling prism 40 is significantly closer to one of the alignment features 350 (as compared to the other of the alignment features 350) than the curved features. In this way, the closer alignment screw 350 mainly effects a lateral displacement of the curved part 20 with respect to the illumination strip on the prism, while the other screw 350 mainly effects a rotation with respect to the same illumination strip. Achieving optimal positioning and alignment of the curved part 20 may occur relatively quickly, for example, using two alignment screws 350 for one to three iterations. A benefit of using the alignment fixture 300, as compared to manual alignment, is that it reduces measurement time, especially where multiple parts of the same or similar shape are to be measured in succession. With such an alignment jig, careful alignment of the first part is sufficient to ensure rapid alignment of all subsequent parts.

Mode spectrum broadening effect

When measuring the curved part 20 in the form of an ideal cylinder as perfectly aligned in the coupling prism assembly 38, the angle of emergence due to coupling is present

A slight broadening of the lines of the TE and TM mode spectra is desired for the curved waveguide of beam 62F of light. Compared with a straight waveguide with a uniform cross sectionThe effective refractive index of the eigenmode of the curved waveguide varies slightly.

The following equation for the effective index change of a rectangular waveguide can be used to estimate the maximum possible broadening due to this effect:

wherein n is₀Is the peak index, 2T is the thickness of the rectangular waveguide, and ρ is the radius of curvature seen by obliquely incident rays. For curved part 20, thickness 2T may be replaced by 0.5DOL to account for the approximately triangular index profile. For a ray impinging on the interface 50 along the plane of incidence,

where R1 is the radius of the cylinder. For a 0.5mm slot the thickness of the slot,

ranging from about-10 to +10 degrees (with the indication as

Maximum angle of

) Although for most light rays the range is from-5 to +5 degrees, so that for R1-8.5 mm, ρ correspondingly takes values greater than 1.1 m. Thus, the widening effect is:

this horizontal line broadening is comparable to the narrowest line observed with FSM-6000LE measurement systems, whose breadth is limited by the optical resolution or leakage nature of the mode in the measurement. This explains why the systems and methods disclosed herein can be used to measure curved parts 20 having a first radius R1 as small as 1 mm. The widening in this case would be at 2x10^–4On the order of magnitude of, nearly to, the smallest modeFormula (ii) interval. This widening is only for those with a small radius R1 (e.g., R1)<2mm) and large DOL are severe and mitigated by using narrow grooves.

The above estimate of modal spectral broadening can be reversed and used to determine the slot width needed to limit the broadening message to a desired value. The allowable broadening is less than about the typical mode spacing Δ n_msAbout 1/3, and in many practical interesting cases about 5 x10^-4RIU. Then, the angular range in radians allowed by the groove

Comprises the following steps:

in many cases, the typical mode interval is inversely proportional to DOL. Having about 1.5X 10 in the ion exchange region 25^- ²In the example of maximum index increments of RIU, about 2 μm per increment of DOL adds an additional mode to the spectrum, so that the typical mode spacing is at

On the order of magnitude of (a). .

Thus, the angular range allowed by the light restriction

Should not be greater than:

in an example, for R1-10 mm, DOL-50 μm, and n₀≈1.52,

So that

Should be less than about 15. This is the limit at which, at this limit,line widening will result in substantial fusion of the lines, which will render their discrimination impractical. The smaller line broadening results in a reduction of the line contrast, resulting in a significant difficulty in intensity-based discrimination for automatic recognition of patterns.

Stricter criteria may be applied, for example

To substantially limit this contrast reduction. In this case, the angular range allowed by the light restriction

Should not be greater than:

and for a typical ion-exchanged glass having a maximum refractive index increment on the order of 0.015RIU and a DOL of 50 μm,

should not be greater than about 10. Finally, to eliminate the effect of line broadening due to coupling into the curved waveguide mode, in an example, in a typical high resolution measurement system, the broadening should be below about 2 × 10^-5RIU, in this case:

for curved parts 20 having a range of values of radius R1, such as a conical surface, the value of R1 at the bottom of the range should be taken for a conservative estimation of the parameters of the light-constraining member 200 based on the disclosed relationship. On the other hand, for a less conservative estimate, any typical value for the bottom half of the range of R1 may allow sufficient performance.

Curved part 20 with R1 as small as 1mm was measured in the allowed directions, R2 was at least 100m to prevent observable line broadening, and at least 20m to avoid significant measurement degradation. Smaller values of R2 may be tolerated if the prism length in the z-direction (see FIG. 1A) is reduced (e.g., from 12mm to between 2 and 4 mm) to limit the angular broadening of the spectral line due to unwanted expansion

In an example, the width w of the illumination area 62L_LMay vary with respect to the length (i.e., z-direction) of the illumination area. As described above, in one example, the slot width of the light-confining member 200 may vary between the front end 202 and the back end 206, while still allowing for substantial improvement in the mode spectral contrast. Specifically, the width s of the slot 220 varying between about (2/3) · s and about (1.5) · s between the front end 202 and the rear end 206 may result in an improvement in contrast similar to a constant width slot.

It will be apparent to those skilled in the art that modifications to the preferred embodiment disclosed herein may be made without departing from the spirit or scope of the invention as defined by the appended claims. Thus, it is intended that the present disclosure cover the modifications and variations of this disclosure provided they come within the scope of the appended claims and their equivalents.

Claims

1. Method for determining at least one property of a part having a bulk refractive index n_sAn outer surface and a refractive index n having a peak refractive index_O>n_sThe ion exchange region of (a), comprising:

by refractive index n_fWill have a refractive index n_pWith the coupling surface of the coupling prism abutting the outer surface to define a coupling interface proximate the near-surface waveguide region, wherein n_p≥n_f>n_s；

Directing measurement light from a light source through the coupling prism and to the coupling interface and coupling a portion of the measurement light into TE and TM modes supported by the near-surface waveguide region;

digitally capturing TE and TM mode spectra from the measurement light reflected from the coupling interface and defined by TE and TM modes supported by the near-surface waveguide region; and

processing the TE and TM mode spectra to determine the at least one characteristic of the near-surface waveguide region of the part.

2. The method of claim 1, wherein n is_f＝n_p。

3. Method according to any of claims 1 to 2, characterized in that n is_O≥n_f>n_s。

4. The method of any of claims 1-2, wherein the TE and TM mode spectra each comprise a series of mode lines.

5. The method of claim 4, wherein the pattern lines comprise bright lines.

6. The method according to any one of claims 1 to 2, wherein the processing comprises:

measuring a position of the pattern line to determine a pattern interval; and

determining the at least one characteristic using the pattern interval.

7. The method of claim 6, wherein the mode spacing is used to determine the TE and TM refractive indices.

8. The method of any one of claims 1 to 2, wherein the at least one characteristic is selected from a group of characteristics comprising: surface stress, stress distribution, compressive stress, depth of layer, refractive index distribution, and birefringence.

9. The method of any of claims 1 to 2, wherein the outer surface of the part is curved.

10. The method of claim 9, wherein the coupling prism has an input surface and an output surface, and further comprising:

directing the measurement light through at least one light confining member operatively arranged with respect to at least one of the input surface and the output surface, wherein the at least one light confining member comprises a groove having a constant or varying width, wherein the groove defines the width of the measurement light, and wherein the width is 3mm or less.

11. Method for determining at least one property of a part having a bulk refractive index n_sAn outer surface and a refractive index n having a compressive stress and a peak refractive index_O>n_sThe ion exchange region of (a), comprising:

by refractive index n_pAnd through a refractive index n arranged between the coupling prism and the outer surface_fThe docking fluid supplies light to the near-surface waveguide region to cause the light to travel as TE and TM guided waves in the near-surface waveguide region, and wherein n_p≥n_f>n_s；

Extracting the TE and TM guided wave light from the near-surface waveguide region through the interfacing fluid and the coupling prism, wherein the extracted light includes a TE component defining a TE mode spectrum having TE mode lines and a TM component defining a TM mode spectrum having TM mode lines;

capturing images of the TE and TM mode spectra;

measuring relative positions of the TE mode line and the TM mode line using the captured image; and

determining at least one characteristic of the near-surface waveguide region of the part using the measured relative positions of the TE mode line and the TM mode line.

12. The method of claim 11, wherein n is_O≥n_f>n_s。

13. The method of any of claims 11 to 12, further comprising using the measured relative positions of the TE and TM mode lines to determine at least one of:

a) TE and/or TM refractive index profiles;

b) a compressive stress at the outer surface;

c) a distribution of compressive stress distribution with respect to distance from the outer surface into the near-surface waveguide region; and

d) birefringence properties.

14. The method of any one of claims 11 to 12, wherein the outer surface of the part has a cylindrical curvature.

15. A prism-coupling system for determining at least one characteristic of a part having a bulk refractive index n_sAn outer surface and a refractive index n having a peak refractive index_O>n_sAnd supports TE and TM waveguide modes:

a light source system that generates measurement light;

a coupling prism assembly having a coupling prism with input and output surfaces and a coupling surface via a coupling surface having an index of refraction n_fTo define a coupling interface proximate the near-surface waveguide region to couple a portion of the measurement light into and output a portion of the measurement light from the TE and TM waveguide modes to define TE and TM mode spectra, respectively, wherein n_p≥n_f>ns；

A detector system arranged to capture images of the TE and TM mode spectra; and

a controller operatively connected to the detector system and configured to process the captured image to determine the at least one characteristic of the near-surface waveguide region of the part.

16. The method of claim 15, wherein the at least one characteristic is selected from a group of characteristics comprising: surface stress, stress distribution, compressive stress, depth of layer, refractive index distribution, and birefringence.

17. A system according to any of claims 15 to 16, wherein n is_O≥n_f>n_s。

18. The system according to any one of claims 15 to 16, wherein the TE and TM spectra comprise TE and TM mode lines, respectively, and wherein the controller is configured to use the image to measure the relative positions of the TE and TM mode lines.

19. The system of claim 18, wherein the controller is configured to use the measured relative positions of the TE mode line and the TM mode line to determine at least one of:

a) TE and/or TM refractive index profiles;

b) surface compressive stress;

c) distribution of compressive stress; and

d) birefringence properties.

20. The system of any of claims 15 to 16, wherein the outer surface of the part is curved, the measurement light has a width, and the system further comprises:

at least one light-confining member operatively arranged with respect to at least one of the input and output surfaces of the coupling prism, wherein the at least one light-confining member comprises a slot having a constant or varying width, wherein the slot defines the width of the measurement light to be 3mm or less.